Asobo has already changed the character limitation to 5 characters. Although they claim it as ICAO, in truth it is simply the internal airport identifier. But, they have been using fake 4-character ICAO codes for some airfields, which would be unnecessary if they expanded the ID to 8 characters. So by keeping it as 5 characters, and using fake IDs, what you fear has already happened by design in the sim. There is no separation as to airport ID and ICAO. They are the same in the sim, and are referenced as ICAO. Arguing over the semantics of the ID is pointless. The damage already exists.
I advocate changing the ID limitation to allow the true airport ID for all the smaller and military airfields, as well as water ports and heliports.
Here’s a link to an airport comparison spreadsheet which compares the “ICAOs” in the sim to the real world identifiers.
AirportsCompare